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Pharmacology > Phamacokinetics 1 > Flashcards

Phamacokinetics 1 Flashcards

1
Q

Define drug absorption

A

the process of transfer of a drug from the site of administration into the systemic circulation

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2
Q

What is the most common route of drug administration?

A

oral

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3
Q

How would you give diazepam for a fitting child - status epilepticus?

A

per rectum

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4
Q

how would you give a dye for an X-ray to look at the coronary arteries?

A

intra-arterial

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5
Q

How would you give an anti-emetic for a vomiting pt?

A

IV

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6
Q

How is insulin administered?

A

subcutaneous

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7
Q

Which route of administration is the exception to the rule that a drug must cross at least one membrane to get into the circulation

A

IV

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8
Q

What are the ways in which a drug can pass across a membrane?

A

passive diffusion through the lipid bilayer
diffusion through pores or ion channels
active transport - carrier mediated
facilitated diffusion - carrier mediated
pinocytosis

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9
Q

What factors determine the rate of passive diffusion?

A

conc gradient
thickness of membrane
SA and permeability of membrane

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10
Q

Which direction does diffusion through pores or ion channels occur - against or down the conc gradient?

A

down the conc gradient

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11
Q

What type of substance travels by diffusion through ion channels or pores?

A

very small water soluble molecules

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12
Q

Give an example of a drug that can diffuse through pores/ion channels and what was it used for?

A

lithium - for manic depression (bipolar)

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13
Q

What two processes come under carrier mediated transport?

A

active transport

facilitated diffusion

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14
Q

What does P-gp (multi-drug resistance MDR1) do?

A

it removes drugs from the cytoplasm to the extracellular side

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15
Q

Name one drug that interacts with P-gp and what this results in

A

Verapamil - increases the concentration of anti cancer drugs in the cytoplasm

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16
Q

What is pinocytosis?

A

A form of endocytosis usually involved in taking up surrounding fluids (and the substances this contains) into the cell

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17
Q

Why is drug ionisation needed?

A

ionic forces form part of the ligand receptor interaction

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18
Q

What does the extent of ionisation of a drug depend on?

A

strength of the ionisable group and the pH of the solution

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19
Q

What is the pKa of a drug?

A

the pH at which half of the substance is ionised and half is unionised

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20
Q

Where are weak acids best absorbed and why?

A

in the stomach, as weak acids are least ionised in acidic conditions

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21
Q

What is an acid?

A

A proton donor

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22
Q

Where are weak bases best absorbed?

A

in the intestine

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23
Q

How do we treat aspirin overdose?

A

administer IV bicarbonate to alkalinise urine, so faster elimination of aspirin

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24
Q

What are the advantages of oral administration?

A

easy
convenient
large SA of s. intestine
large blood supply of s.intestine so rapid adsorbtion

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25
Q

What factors affect oral absorption?

A

drug structure
drug formulation
gastric emptying
1st pass metabolism

26
Q

How does drug structure influence oral adsorption?

A

lipid solubility - needs to be lipid soluble to be absorbed from the gut
polarisation - highly polarised drugs only partially absorbed and the rest goes into the faeces
instability at low pH or when there is digestive enzymes

27
Q

How does drug formulation affect oral absorption?

A

modified release tablets dissolve slowly or have an enteric coating

28
Q

what factors affect the rate of gastric emptying?

A

food
trauma
gastric surgery

29
Q

What are the barriers that an oral drug has to go through to reach the systemic circulation?

A

intestinal lumen
intestinal wall
liver

30
Q

What factors in the lumen hinder drug absorption?

A

digestive enzymes

colonic bacteria

31
Q

What factors of the intestinal wall affect drug absorprion?

A

Monoamine oxidases are affected by foods
efflux transporters eg P-gp on enterocytes
short gut syndrome produced by extensive bowel surgery

32
Q

Give an example of a drug that is taken up by pinocytosis?

A

Amphotericin (antifungal)

33
Q

Which methods of drug administration avoid first pass?

A 
per rectum
IV
sublingual
intramuscular
inhalation
transdermal
34
Q

Give an example of a drug which is given transcutaneously

A

Fentanyl

35
Q

What are the disadvantages to transcutaneous?

A

limited rate and extent of absorption

36
Q

what are the advantages of transcutaneous?

A

slow and continued absorption, good for drugs that need a long lasting effect

37
Q

What are the advantages of intradermal and subcut?

A

avoids the stratum corneum
small volume can be given
local effect
can deliberately limit rate of absorption of drugs

38
Q

What factor is intradermal and subcut absorption limited by?

A

blood flow

39
Q

For what are depot injections used?

A

mental health

40
Q

What are the advantages of the intranasal route?

A

low levels of proteases and drug metabolising enzymes
good SA
can be used for local or systemic effects

41
Q

What are the a advantages of inhalational methods?

A

large SA

large blood flow

42
Q

What are the limitations of inhalational methods

A

risk of toxicity to alveoli

difficult to deliver non-volatile drugs

43
Q

What is the definition of distribution?

A

The process by which the drug is transferred reversibly from the general circulation to the tissues as the blood concentration increases and then returns from the tissues to the blood when the blood concentration falls

44
Q

What two types of protein can drugs bind to?

A

plasma proteins

tissue proteins

45
Q

Which protein is involved in the commonest type of protein binding?

A

albumin

46
Q

Protein binding is always reversible? T or F

A

F - it can be irreversible eg some cytotoxic chemo drugs

47
Q

Which types of drugs, lipid soluble or water soluble pass easier through the BBB?

A

lipid soluble drugs

48
Q

Which drugs use the solute carreris that supply the brain with nutrients?

A

L-Dopa for parkinsons

49
Q

How are drugs removed from the brain?

A

diffusion into the plasma
active transport into the choroid plexus
elimination in CSF

50
Q

Which type of drugs, lipid or water soluble, cross the placenta easily?

A

lipid soluble drugs

51
Q

What two processes are involved in elimination?

A

metabolism

excretion

52
Q

What is metabolism of a drug?

A

the transformation of the drug molecule into a different molecule

53
Q

What are the three states of excretion?

A

solid
liquid
gas

54
Q

What are phase 1 reactions?

A

transformation of a drug into a more polar metabolite
done by unmasking or adding a functional group
oxidations are the commonest reaction
carried out mainly by CYP450 enzymes

55
Q

Where are cyp450 enzymes present

A

in the smooth endoplasmic reticulum of the liver

56
Q

What are phase 2 reactions?

A

conjugation - formation of a covalent bond between the drug/phase 1 metabolite an dan endogenous substrate eg glucoronic acid.
the resulting products are less active and readily excreted by the kidneys

57
Q

What type of compounds are excreted in fluid form?

A

low molecular weight

polar

58
Q

What type of compounds are excreted in solid form?

A

high MWT compounds

59
Q

What type of compounds are excreted as gases?

A

volatile

60
Q

what are the fluid forms of excretion?

A

urine , bile , sweat , tears , breast milk

61
Q

What are the solid forms of excretion?

A

faeces and hair

62
Q

What is the eqn for total excretion?

A

total excretion = glomerular filtration + tubular secretion - reabsorption

Pharmacology (10 decks)

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